Projected Cutting Dates for Black Cutworms

April 28, 2000
Although many acres of corn remain to be planted throughout the state, it is not too early to begin thinking about well-timed scouting efforts for black cutworms. In issue no. 2 of the Bulletin, Kevin Steffey laid out some of the fundamentals regarding black cutworm biology and offered some tips on the correct interpretation of intense captures of moths with pheromone traps. In issue no. 4, Kevin reminded our readers that projected cutting dates of black cutworms are based on intense captures (eight to nine moths in a 1- to 2-night period) of moths caught in wing traps (sticky bottoms), not bucket traps. Robert Scott, a scientist with the Illinois State Water Survey, uses intense captures of black cutworm moths to begin projecting when 300 heat units above a base temperature of 50°F will accumulate. These projections depend on historical temperature records for sites throughout Illinois. Table 1 provides some projected cutting dates for 20 counties in which cooperators have reported intense flights this spring. It should not be inferred that intense captures have not occurred in counties or areas of the state not listed in Table 1. Noticeably absent are intense capture reports from southern Illinois. I am reasonably confident that intense captures have occurred below Interstate 70, but we just haven't had any confirmations. We greatly appreciate receiving reports of intense captures from the field so that we can provide our readers with the most accurate projected cutting dates possible. So if you are located south of Interstate 70 and monitor a trap, we would be pleased to pass along the information.

Based on Robert Scott's projected cutting dates, producers may begin to see cutting of plants as early as May 8 in western Illinois. Cutting may begin in earnest by mid-May in many central and northern counties. In essence, don't be surprised to see fourth-larval instars in some fields after the first week of May, especially in western Illinois. Cornfields most at risk to economic injury include those with plants at or below the 4-leaf stage of development. We encourage our readers to remain watchful for potential cutworm injury, especially as the projected cutting dates in Table 1 draw near. However, don't wait to begin scouting cornfields until mid-May. Instead, look for early signs of black cutworm leaf feeding (small pinholes of leaf tissue removed) caused by less mature black cutworm larvae (instars 1 to 3). We'll continue to provide more black cutworm management tips as we move into early May.--Mike Gray

Author: Mike Gray